There is a need within the aviation industry, for example, to heat-treat various types of workpieces. When various components, such as, for example, plates, are joined together by soldering, the components are heated in an evacuated oven. The oven is evacuated in order to create a vacuum in the oven and thereby lower the partial pressure for the unwanted chemical compounds which would otherwise react with the workpiece and cause contamination of the workpiece. Despite the fact that many vacuum ovens can have low pressures, they often have leaks in the construction which cause or permit air to filter or seep into the oven. For many types of materials, the pressure in such ovens is nevertheless sufficiently low for the oven to be able to be used to perform the heat treatment with the desired result. This means, however, that oven leaks often remain undetected and unsealed, since it is not profitable to try and obtain a better vacuum.
Workpieces made of highly contamination-sensitive materials, such as various titanium alloys, cannot, however, be heat-treated in such “leaky,” and hence contaminated ovens. The properties of these materials are impaired even at relatively low partial pressures of certain contaminants, such as, for example, oxygen. Apart from the measures to increase pump capacity for evacuation of the oven or to make the oven as leak-tight as possible, an inert gas can be used to avoid contamination of the workpiece.
A related method is disclosed in DT 24 48 714 A1 which utilizes a protective gas. In this method, the partial pressures of unwanted gases are controlled by a flow of protective gas, such as argon, streaming continuously through the oven. The method does, however, have drawbacks. One drawback is that the purity of the oven atmosphere is determined by the purity of the protective gas. There are always contamination products present in a protective gas and these will be fed continuously to the oven together with the other gas. The oven is also required to be suitable for use of a protective gas, which means, in turn, that an existing oven may need to be modified; i.e., it is not possible to use just any vacuum oven, but rather the oven is required, for example, to have necessary gas connections. Moreover, a continuous flushing of the oven using a highly pure gas entails high gas consumption and for that reason involves substantial costs.